Groundwater and surface water contributions to metals loading in Bayhorse Creek at the abandoned Ramshorn Mine site near Bayhorse, Idaho.

摘要

Many abandoned mines in the United States are littered with waste metals that leach into watersheds and degrade habitats. Although metals-laden waters may appear pristine, fish bioaccumulate high concentrations of metals in their tissues, which create health risks if consumed by humans. This study examines the source and fate of metals in Bayhorse Creek near the abandoned Ramshorn mine outside of Challis, Idaho. In 2003, the U.S. Geological Survey found high levels of arsenic, cadmium, chromium, copper, lead, silver, and zinc in soils adjacent to the tailings pile. The Idaho Department of Environmental Quality authorized remediation to begin in summer 2011 without fully comprehending the source and fate of contaminants into the creek.;Metals loads were determined along the reach of Bayhorse Creek adjacent to the mine by measuring the flow rates of streams and groundwater seeps, and collecting water samples for chemical analysis. The chemical controls on metals mobility and attenuation in the surface and groundwater at the site were determined by computer modeling, a diffuse double-layer surface complexation model and the geochemical program PHREEQC.;Dissolved and suspended arsenic, copper, iron, manganese, lead, and zinc load the creek. The lowest site along the creek consistently measured as the highest load. Arsenic, copper, and lead loads were relatively insignificant compared to iron and manganese. The results indicate that 47% or more of the iron and manganese travel as metal-oxides, and arsenic and zinc tend to sorb to ferrous oxides. Large metals fluxes between SW-1 and SW-5 and at SW-8 suggest tailings and waste rock located between SW-1 and SW-5 and the slag pile adjacent to SW-8 are the main sources of metals contamination. Concentrations below the EPA drinking water standards and the absence of acidic pH indicate that the main metals loading consists of safe levels of iron, manganese, and zinc.